Process for the preparation of spiro[2.5]octane-5,7-dione and spiro[3.5]nonane-6,8-dione

ABSTRACT

This invention relates to methods for the synthesis of spiro[2.5]octane-5,7-dione and spiro[3.5]nonane-6,8-dione which are useful as intermediates in the manufacture of pharmaceutically active ingredients.

RELATED APPLICATIONS

The application claims the priority to PCT ApplicationPCT/CN2014/086143, filed on Sep. 9, 2014.

TECHNICAL FIELD

This invention relates to methods for the synthesis ofspiro[2.5]octane-5,7-dione and spiro[3.5]nonane-6,8-dione which areuseful as intermediates in the manufacture of pharmaceutically activeingredients.

BACKGROUND

The compounds spiro[2.5]octane-5,7-dione and spiro[3.5]nonane-6,8-dioneare useful and important intermediates for the preparation ofpharmaceutically active substances. Several routes to them are known andare quite challenging. However, they all suffer from severe drawbacksfrom a chemical process point of view. Therefore, it is a demand fordeveloping efficient and robust methods to synthesizespiro[2.5]octane-5,7-dione and spiro[3.5]nonane-6,8-dione in order tocircumvent these problems.

Up to now, several routes to synthesize spiro[2.5]octane-5,7-dione andspiro[3.5]nonane-6,8-dione have been described in published papers orpatents applications.

WO 2012052451 and WO 2012085166 describe a four-step (two operations)synthesis of spiro[2.5]octane-5,7-dione (3) via Wittig reaction,Michael/Claisen reactions followed by hydrolysis and decarboxylationusing (1-ethoxycyclopropoxy)trimethylsilane (1) as the starting material(Scheme 1). The disadvantage of this approach is that flashchromatography is used for the purification of intermediate and finalproduct, which is not practical for scale-up. Additionally, the use ofo-dichlorobenzene and sodium hydride which is used quite often onlaboratory scale is not ideal in the pilot or manufacture scale either.

Angew. Chem. Intl. Ed., 38(22), 3373-3375, 1999 describes the synthesisof spiro[3.5]nonane-6,8-dione (6) via a similar protocol as above. Thestarting material is cyclobutanone (4). Due to the less activity of theWittig reagent (MeC(O)CH═PPh₃) and the low volatile property ofcyclobutanone (4), the first step can only be carried out at 100° C. toincrease the reactivity and in silicon oil to avoid the loss ofcyclobutanone (4) from the reaction system. After the reaction, theenone (5) has to be distilled out from the silicon oil in order toproceed to the next step (Scheme 2).

Org. Proc. Res. Dev. 7(6), 913-916, 2003 describes synthesis ofspiro[3.5]nonane-6,8-dione (6) via hexenone (7) (Scheme 3).

Therefore, there is a strong need for developing a novel and practicalprocess to synthesize spiro[2.5]octane-5,7-dione (3) and/orspiro[3.5]nonane-6,8-dione (6), which could allow to use the abovementioned starting materials ((1-ethoxycyclopropoxy)trimethylsilane (1)and/or cyclobutanone (4)) and provide the desired products in highquality and good chemical yield without involvement of chromatographypurification and usage of uncommon organic solvents and reagents.

DESCRIPTION OF THE INVENTION

The present invention provides two independent efficient processes forthe synthesis of spiro[2.5]octane-5,7-dione (via Process A or Process B)and/or spiro[3.5]nonane-6,8-dione (via Process A) as described hereinbelow.

A general process for preparing spiro[2.5]octane-5,7-dione is outlinedin Scheme 4. In one embodiment, the present invention is directed to thegeneral multi-step synthetic method for preparingspiro[2.5]octane-5,7-dione as set forth in Scheme 4 below. In otherembodiments, the invention is directed to each of the individual stepsof Scheme 4 and any combination of two or more successive steps ofScheme 4. The invention may also be directed to the intermediatecompounds, e.g. as set forth in Scheme 4.

In Scheme 4, the substituent R may be independently selected from alkyl,such as e.g. independently selected from C1-C6 alkyl, preferably C1-C4alkyl (such as e.g. methyl, ethyl, propyl, isopropyl, or the like), morepreferably C1-C3 alkyl or even more preferably C1-C2 alkyl, particularlyethyl.

Accordingly, in Scheme 4 the group C(O)OR represents an ester group,preferably an alkyl ester group, where R may be independently selectedfrom alkyl, such as e.g. independently selected from C1-C6 alkyl,preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl, isopropyl,or the like), more preferably C1-C3 alkyl or even more preferably C1-C2alkyl, particularly ethyl.

Thus, in one aspect, the present invention relates to a process for themanufacture of spiro[2.5]octane-5,7-dione having the formula

said process comprising the following steps (Scheme 4′):

For example, certain embodimental details may be one or more of thefollowing (Scheme 4″):

Accordingly, the present invention further relates to one or more of theabove steps of Scheme 4, 4′ or 4″ as well as to one or more of aboveintermediates of Scheme 4, 4′ or 4″.

With reference to the steps shown in Scheme 4, 4′ and 4″ of theinvention, a process or method according to the present inventioncomprises one or more of the following:

-   -   reacting a (1-alkoxycyclopropoxy)trimethylsilane [e.g.        (1-ethoxycyclopropoxy)trimethylsilane (1)] with a Wittig        reagent (9) to form a cyclopropylidene carboxylic acid alkyl        ester [e.g. cyclopropylidene carboxylic acid ethyl ester (10)]        (such as e.g. in the presence of a suitable acid, such as acetic        acid, in a suitable solvent, such as high boiling point solvent        (e.g. tetraethylene glycol dimethyl ether). Preferably, a high        boiling point solvent (such as tetraethylene glycol dimethyl        ether) is used in this step in order to purify the low boiling        point product by distillation and make it more practical in a        plant),    -   cyclizing cyclopropylidene carboxylic acid alkyl ester [e.g.        cyclopropylidene carboxylic acid ethyl ester (10)] with dialkyl        1,3-acetonedicarboxylate [e.g. diethyl 1,3-acetonedicarboxylate]        to form 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid dialkyl        ester [e.g. 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid        diethyl ester (11), which may be isolated or not] (such as e.g.        in the presence of a suitable organic or inorganic base (e.g.        K₂CO₃ followed by EtONa) in a suitable solvent, such as K₂CO₃ in        THF, followed by addition of EtONa in EtOH), saponification        (ester hydrolysis) of (isolated or non-isolated)        5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid dialkyl ester        [e.g. 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid diethyl        ester (11)] with the aid of a suitable base (such as alkali        hydroxide, e.g. aqueous KOH) and decarboxylation (e.g. under        acidic conditions, such as by heating with HCl) to form        spiro[2.5]octane-5,7-dione (3),    -   optionally, crystallization or recrystallization of crude        spiro[2.5]octane-5,7-dione (3) such as from MTBE (methyl        tert-butyl ether) to obtain purified spiro[2.5]octane-5,7-dione        (3).

The yield is 42%-50% (from intermediate 10) and the purity is >98%purity without any chromatography.

A general process for preparing spiro[3.5]nonane-6,8-dione is outlinedin Scheme 5. In one embodiment, the present invention is directed to thegeneral multi-step synthetic method for preparingspiro[3.5]nonane-6,8-dione as set forth in Scheme 5 below. In otherembodiments, the invention is directed to each of the individual stepsof Scheme 5 and any combination of two or more successive steps ofScheme 5. The invention may also be directed to the intermediatecompounds, e.g. as set forth in Scheme 5.

Scheme 5: Process for the manufacture of spiro[3.5]nonane-6,8-dioneaccording to the invention (aspect 2 of the invention):

In Scheme 5, the substituent R may be independently selected from alkyl,such as e.g. independently selected from C1-C6 alkyl, preferably C1-C4alkyl (such as e.g. methyl, ethyl, propyl, isopropyl, or the like), morepreferably C1-C3 alkyl or even more preferably C1-C2 alkyl, particularlyethyl.

Accordingly, in Scheme 5 the group C(O)OR represents an ester group,preferably an alkyl ester group, where R may be independently selectedfrom alkyl, such as e.g. independently selected from C1-C6 alkyl,preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl, isopropyl,or the like), more preferably C1-C3 alkyl or even more preferably C1-C2alkyl, particularly ethyl.

Thus, in another aspect, the present invention relates to a process forthe manufacture of spiro[3.5]nonane-6,8-dione having the formula

said process comprising the following steps (Scheme 5′):

For example, certain embodimental details may be one or more of thefollowing (Scheme 5″):

Accordingly, the present invention further relates to one or more of theabove steps of Scheme 5, 5′ or 5″ as well as to one or more of aboveintermediates of Scheme 5, 5′ or 5″.

With reference to the steps shown in Scheme 5, 5′ and 5″ of theinvention, a process or method according to the present inventioncomprises one or more of the following:

-   -   cyclizing cyclobutylidene carboxylic acid alkyl ester [e.g.        cyclobutylidene carboxylic acid ethyl ester (12), cf. WO        2004/054564] with dialkyl 1,3-acetonedicarboxylate [e.g. diethyl        1,3-acetonedicarboxylate] to form        6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid dialkyl ester        [e.g. 6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid diethyl        ester (13), which may be isolated or not] (such as e.g. in the        presence of a suitable organic or inorganic base (e.g. NaH        followed by EtONa) in a suitable solvent, such as NaH in THF,        followed by addition of EtONa in EtOH),    -   saponification (ester hydrolysis) of (isolated or non-isolated)        6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid dialkyl ester        [e.g. 6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid diethyl        ester (13)] with the aid of a suitable base (such as alkali        hydroxide, e.g. aqueous KOH) and decarboxylation (e.g. under        acidic conditions, such as by heating with HCl) to form        spiro[3.5]nonane-6,8-dione (6),    -   optionally, crystallization or recrystallization of crude        spiro[3.5]nonane-6,8-dione (3) such as from MTBE (methyl        tert-butyl ether) to obtain purified spiro[3.5]nonane-6,8-dione        (6).

The overall yield is about 45% from intermediate (12).

Alternatively, a general process for preparingspiro[2.5]octane-5,7-dione is outlined in Scheme 6. In one embodiment,the present invention is directed to the general multi-step syntheticmethod for preparing spiro[2.5]octane-5,7-dione as set forth in Scheme 6below. In other embodiments, the invention is directed to each of theindividual steps of Scheme 6 and any combination of two or moresuccessive steps of Scheme 6. The invention may also be directed to theintermediate compounds, e.g. as set forth in Scheme 6.

In Scheme 6, the substituents R and R′ may be independently selectedfrom alkyl, such as e.g. independently selected from C1-C6 alkyl,preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl, isopropyl,or the like), more preferably C1-C3 alkyl or even more preferably C1-C2alkyl, particularly R is ethyl and/or R′ is methyl.

Accordingly, in Scheme 6 the groups C(O)OR and C(O)OR′ represent anester group, respectively, preferably an alkyl ester group, where R andR′ may be independently selected from alkyl, such as e.g. independentlyselected from C1-C6 alkyl, preferably C1-C4 alkyl (such as e.g. methyl,ethyl, propyl, isopropyl, or the like), more preferably C1-C3 alkyl oreven more preferably C1-C2 alkyl, particularly R is ethyl and/or R′ ismethyl.

Thus, in another aspect, the present invention relates to a process forthe manufacture of spiro[2.5]octane-5,7-dione having the formula

said process comprising the following steps (Scheme 6′):

For example, certain embodimental details may be one or more of thefollowing (Scheme 6″):

Accordingly, the present invention further relates to one or more of theabove steps of Scheme 6, 6′ or 6″ as well as to one or more of aboveintermediates of Scheme 6, 6′ or 6″.

With reference to the steps shown in Scheme 6, 6′ and 6″ of theinvention, a process or method according to the present inventioncomprises one or more of the following:

-   -   reacting cyclopropylidene carboxylic acid alkyl ester [e.g.        cyclopropylidene carboxylic acid ethyl ester (10)] with alkyl        acetoacetate [e.g. ethyl acetoacetate] to form        2-(1-alkoxycarbonylmethyl-cyclopropyl)-3-oxo-butyric acid alkyl        ester [e.g. 2-(1-ethoxycarbonylmethyl-cyclopropyl)-3-oxo-butyric        acid ethyl ester (14)], which may be isolated or not] (such as        e.g. in the presence of a suitable organic or inorganic base        (e.g. K₂CO₃) in a suitable solvent, such as K₂CO₃ in THF),        saponification (ester hydrolysis) of (isolated or non-isolated)        2-(1-alkoxycarbonylmethyl-cyclopropyl)-3-oxo-butyric acid alkyl        ester [e.g. 2-(1-ethoxycarbonylmethyl-cyclopropyl)-3-oxo-butyric        acid ethyl ester (14)] with the aid of a suitable base (such as        alkali hydroxide, e.g. aqueous NaOH) and decarboxylation (e.g.        under acidic conditions, such as by heating with HCl) to form        [1-(2-oxo-propyl)cyclopropyl]acetic acid (15),    -   esterification of [1-(2-oxo-propyl)cyclopropyl]acetic acid (15)        to form [1-(2-oxo-propyl)cyclopropyl]acetic acid alkyl ester        [e.g. [1-(2-oxo-propyl)cyclopropyl]acetic acid methyl ester        (16)] (such as in methanol in the presence of HCl),    -   cyclizing [1-(2-oxo-propyl)cyclopropyl]acetic acid alkyl ester        [e.g. [1-(2-oxo-propyl)cyclopropyl]acetic acid methyl ester        (16)] to form spiro[2.5]octane-5,7-dione (3) (such as e.g. in        the presence of a suitable organic or inorganic base (e.g. MeONa        in MeOH),    -   optionally, crystallization or recrystallization of crude        spiro[2.5]octane-5,7-dione (3) such as from MTBE (methyl        tert-butyl ether) to obtain purified spiro[2.5]octane-5,7-dione        (3).

Spiro[2.5]octane-5,7-dione (3) is obtained in a 62% yield with 98.6%HPLC purity.

When this protocol is used starting from Compound 12, the major isolatedproduct from this reaction is Compound 18 instead of Compound 17. It isassumed that the Michael Addition intermediate goes through areminiscent Billys-Hillman type reaction (Scheme 7).

In certain more detailed embodiments of the invention, the presentinvention relates to the process and/or the individual process stepssubstantially as described by way of example in the following examples.

Further, the invention relates to a compound useful as intermediateselected from:

or a tautomer or salt thereof.

Furthermore, the invention relates to a compound useful as intermediateselected from:

in each of which R and/or R′ may be independently hydrogen or C1-C6alkyl, preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl,isopropyl, or the like), more preferably C1-C3 alkyl or even morepreferably C1-C2 alkyl, particularly R is ethyl and/or R′ is methyl, ora tautomer or salt thereof.

In a further embodiment, the present invention is not limited to the useof a ethyl or methyl ester of formula

within the processes or methods according to the present invention; inaddition to the respective ethyl esters, a broader genus of esters offormula

in each of which R and/or R′ may be independently C1-C6 alkyl,preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl, isopropyl,or the like), more preferably C1-C3 alkyl or even more preferably C1-C2alkyl, particularly R is ethyl and/or R′ is methyl, may be considered.

Accordingly, in alternative embodiments, the present invention refers toprocesses or methods as disclosed herein above or herein below (e.g.Scheme 1 or Scheme 2) wherein a compound of formula

in each of which R and/or R′ is independently C1-C6 alkyl, preferablyC1-C4 alkyl (such as e.g. methyl, ethyl, propyl, isopropyl, or thelike), more preferably C1-C3 alkyl or even more preferably C1-C2 alkyl,particularly R is ethyl and/or R′ is methyl, is used or involved insteadof a compound of formula

respectively.

In certain embodiments, the present invention relates to an indicatedintermediate or final compound in isolated form, such as e.g. in solid,amorphous or crystalline form.

In certain embodiments, the present invention relates to an indicatedintermediate in solution form (such as e.g. present in a reactionsolvent).

Further, the present invention relates to spiro[2.5]octane-5,7-dione orspiro[3.5]nonane-6,8-dione each obtainable or obtained by a process ormethod according to the present invention.

In an embodiment, the present invention relates tospiro[2.5]octane-5,7-dione isolated (e.g. crystallized) from MTBE(methyl tert-butyl ether).

In an embodiment, the present invention relates tospiro[3.5]nonane-6,8-dione isolated (e.g. crystallized) from MTBE(methyl tert-butyl ether).

Further, the present invention relates in particular to a process forpreparing spiro[2.5]octane-5,7-dione having the formula

comprising one or more of the following:

-   -   cyclization of cyclopropylidene carboxylic acid alkyl ester        having the formula

e.g. cyclopropylidene carboxylic acid ethyl ester, with dialkyl1,3-acetonedicarboxylate having the formula

e.g. diethyl 1,3-acetonedicarboxylate, to form5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid dialkyl ester havingthe formula

e.g. 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid diethyl ester,wherein R may be independently C1-C6 alkyl, preferably C1-C4 alkyl (suchas e.g. methyl, ethyl, propyl, isopropyl, or the like), more preferablyC1-C3 alkyl or even more preferably C1-C2 alkyl, particularly R isethyl;

-   -   ester hydrolysis and decarboxylation of        5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid dialkyl ester        having the formula

e.g. 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid diethyl ester, toform spiro[2.5]octane-5,7-dione, wherein R may be independently C1-C6alkyl, preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl,isopropyl, or the like), more preferably C1-C3 alkyl or even morepreferably C1-C2 alkyl, particularly R is ethyl.

Further, the present invention relates in particular to a process forpreparing spiro[3.5]nonane-6,8-dione having the formula

comprising one or more of the following:

-   -   cyclization of cyclobutylidene carboxylic acid alkyl ester        having the formula

e.g. cyclobutylidene carboxylic acid ethyl ester, with dialkyl1,3-acetonedicarboxylate having the formula

e.g. diethyl 1,3-acetonedicarboxylate, to form6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid dialkyl ester havingthe formula

e.g. 6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid diethyl ester,wherein R may be independently C1-C6 alkyl, preferably C1-C4 alkyl (suchas e.g. methyl, ethyl, propyl, isopropyl, or the like), more preferablyC1-C3 alkyl or even more preferably C1-C2 alkyl, particularly R isethyl;

-   -   ester hydrolysis and decarboxylation of        6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid dialkyl ester        having the formula

e.g. 6,8-dioxo-spiro[3.5]nonane-5,7-dicarboxylic acid diethyl ester, toform spiro[3.5]nonane-6,8-dione, wherein R may be independently C1-C6alkyl, preferably C1-C4 alkyl (such as e.g. methyl, ethyl, propyl,isopropyl, or the like), more preferably C1-C3 alkyl or even morepreferably C1-C2 alkyl, particularly R is ethyl.

Further, the present invention relates in particular to a process forpreparing spiro[2.5]octane-5,7-dione having the formula

comprising one or more of the following:

-   -   cyclization of [1-(2-oxo-propyl)cyclopropyl]acetic acid alkyl        ester having the formula

e.g. [1-(2-oxo-propyl)cyclopropyl]acetic acid methyl ester, to formspiro[2.5]octane-5,7-dione,wherein R′ may be independently C1-C6 alkyl, preferably C1-C4 alkyl(such as e.g. methyl, ethyl, propyl, isopropyl, or the like), morepreferably C1-C3 alkyl or even more preferably C1-C2 alkyl, particularlyR′ is methyl.

The intermediates and final compounds of the invention may be obtainedusing methods of synthesis known in principle, or analogously orsimilarly to known procedures. Preferably, the intermediates involvedand the final compounds may be obtained by the following methodsaccording to the invention which are described in more detailed exampleherein after.

The process steps may be performed substantially as described herein byway of example. A process or method of this invention may comprise oneor more steps of converting and/or reacting the mentioned intermediateswith the appropriate reaction partners, suitably under conditions asdisclosed herein (e.g. by using the indicated reagents and/or solventsand/or temperatures, etc.).

Optimum reaction conditions and reaction times may vary depending on theparticular reactants used. Unless otherwise specified, solvents,temperatures, pressures, and other reaction conditions may be readilyselected by one of ordinary skill in the art. Specific procedures areprovided in the Synthetic Examples section. Typically, reaction progressmay be monitored by gas chromatography (GC), High Pressure LiquidChromatography (HPLC) or Thin Layer Chromatography, if desired.

SYNTHETIC EXAMPLES

In order that this invention be more fully understood, the followingexamples are set forth. These examples are for the purpose ofillustrating preferred embodiments of this invention, and are not to beconstrued as limiting the scope of the invention in any way.

Example 1: Preparation of Cyclopropylidene Carboxylic Acid Ethyl Ester(Compound 10)

To a mixture solution of 100 g of1-ethoxy-1-(trimethylsiloxy)cyclopropane (1) and 17.1 g AcOH in 400 mLtetraethylene glycol dimethyl ether, was added 180 g(2-ethoxy-2-oxoethylidene)triphenylphosphorane which was dissolved in270 mL of dichloromethane dropwise at 90-100° C. for 3 h. During theadding period, dichloromethane was removed by distillation to keep theprocess temperature at 90-100° C. The mixture was stirred at 90-100° C.for another 1 h, which allowed dichloromethane be removed completely bydistillation. Then the product (10) was purified by fractionaldistillation at 10 mbar (cooling temperature of fluid in condensershould not be above −10° C., all distillate was collected as theproduct). A total 50-55 g (yield: 69-76%) of Compound 10 was obtained asa colorless liquid. ¹H NMR (400 MHz, DMSO-d₆) δ 6.22 (m, 1H), 4.13 (q,2H, J=7.2 Hz), 1.45-1.38 (m, 2H), 1.30-1.20 (m, 2H), 1.22 (t, 3H, J=7.2Hz); ¹³C NMR (100 MHz, CDCl₃) δ 165.7, 144.5, 110.4, 59.6, 20.1, 13.7,13.5; MS (m/z) [M-28] 98.1.

Example 2: Preparation of Spiro[2.5]octane-5,7-dione (Compound 3)

To a mixture slurry of K₂CO₃ (43.8 g) in THF (200 mL), were addeddiethyl acetonedicarboxylate (76.9 g) and compound 10 (40.0 g) dropwiserespectively at 20-30° C. The mixture was stirred at 20-30° C. for 1 h.A total of 215.7 g of NaOEt solution (20% in EtOH) was added dropwise atbelow 40° C. for 30 min. The mixture was refluxed for 3 h. A total of354.7 g of KOH solution (20% in water) was added slowly to keep thereaction mixture at slight reflux. The reaction mixture was thenrefluxed for 5 h. The organic solvent in reaction mixture was removed atreduced pressure. The resulting aqueous phase was washed with MTBE(2×100 mL). Then the aqueous phase was heated to 50-60° C., at thistemperature conc. HCl was added dropwise until pH was adjusted to2.5-3.0. It was stirred for another 1 h, and then cooled to 20-30° C.Water (200 mL) was added and the resulting aqueous solution wasextracted with MTBE (3×300 mL). The combined organic phase wasconcentrated under vacuum. Then, another 30 mL of MTBE was added to theresidue, and slurry was stirred for 30 min at 0-10° C., the firstportion of the product was collected by filtration. The filtrate wasconcentrated under vacuum again and then 20 mL of MTBE was added. Afterthe slurry was stirred at 0-10° C. for 0.5 h, the second portion of theproduct was also collected by filtration. The combined product waswashed with 5 mL of MTBE, and then dried under vacuum. A total of 19.5 g(44% yield, 99% purity) of Compound 3 was obtained as a white solid. ¹HNMR (400 MHz, DMSO-d₆) δ 11.05 (s, br 1H), 5.25 (s, 1H), 2.15 (s, 4H),0.35 (s, 4H); ¹³C NMR (100 MHz, DMSO-d₆) δ 178.61, 103.96, 41.76, 14.95,10.85; MS (m/z) 138.1.

Example 3: Preparation of Cyclobutylidene Carboxylic Acid Ethyl Ester(Compound 12)

To a slurry of NaH (8.0 g, 60% in oil) in THF (150 mL), was addedtriethyl phosphonoacetate (44.8 g) in 25 mL of THF dropwise at 0-10° C.over 40 min. The reaction mixture was stirred at 0-10° C. for another0.5 h. Then cyclobutanone (14.0 g) in 25 mL of THF was added dropwise at0-10° C. over 30 min. The reaction mixture was stirred at 0-10° C. for 2h. A total of 50 mL of water was then added slowly at 20-30° C. Theorganic solvent was removed under reduced pressure followed by additionof 150 mL of water. The aqueous solution was extracted with MTBE (3×100mL). The combined organic phase was washed with water (100 mL). It wasthen dried over anhydrous MgSO₄. Filtration followed by evaporation gavethe crude product, which was purified by fractional distillation at81-82° C./19 mbar to give 22.2 g (79% yield, 99% purity) of Compound 12as a colorless liquid. ¹H NMR (400 MHz, CDCl₃) δ 5.56 (m, 1H), 4.13 (q,2H, J=7.2 Hz), 3.12 (m, 2H), 2.81 (m, 2H), 2.08 (m, 2H), 1.25 (t, 3H,J=7.2 Hz); ¹³C NMR (100 MHz, DMSO-d₆) δ 167.2, 165.3, 111.8, 58.9, 33.3,31.8, 17.1, 14.0; MS (m/z) 140.1.

Example 4: Preparation of Spiro[3.5]nonane-6,8-dione (Compound 6)

To a slurry of NaH (0.96 g, 60% in oil) in THF (5.0 mL), was addeddiethyl acetonedicarboxylate (2.4 g) slowly at 0-15° C. After it wasstirred for 0.5 h, a total of 1.4 g of Compound 12 was added slowly at0-15° C. The mixture was stirred at 20-30° C. for 1 h, and then heatedto reflux. 5 mL of EtOH and 2.4 g of NaOEt solution (20% in EtOH) wereadded respectively. The resulting mixture was refluxed for 5 h. Afterthat, a total of 11.2 g of KOH solution (20% in water) was added slowly,and the reaction mixture was continuously refluxed for another 5 h. Theorganic solvent in reaction mixture was removed under vacuum. Theaqueous solution was extracted with MTBE (2×10 mL) and then heated to50-60° C. with addition of conc. HCl until pH at 2.5-3.5. The resultingmixture was stirred at 50-60° C. for 2 h and then cooled to 20-30° C. Itwas extracted with dichloromethane (3×25 mL). The combined organic phasewas concentrated under vacuum. Then 5.0 mL of MTBE was added to theresidue and the resulting slurry was stirred for 0.5 h at 0-10° C. Thesolid was collected by filtration, washed with MTBE (5.0 mL), and driedunder vacuum. A total of 0.68 g (45% yield, 98% purity) of Compound 6was obtained as a white solid. ¹H NMR (400 MHz, DMSO-d₆) δ 11.02 (br s,1H), 5.17 (s, 1H), 2.45-2.25 (m, 4H), 1.90-1.75 (m, 2H), 1.75-1.65 (m,4H); ¹³C NMR (100 MHz, DMSO-d₆) δ 186.22, 103.55, 44.69, 38.35, 31.48,14.61; MS (m/z) 152.1.

Example 5: Preparation of [1-(2-Oxo-propyl)cyclopropyl]acetic Acid(Compound 15)

To a solution of ethyl acetoacetate (48.8 g) in THF (315.0 mL) was addedK₂CO₃ (51.8 g) under nitrogen, the mixture was heated up to 65° C. Atotal of 41.23 g of cyclopropylidene acetic acid ethyl ester was addeddropwise over 30 min, the reaction mixture was stirred for another 3 hat 65° C. Then, a total of 114.0 g (35% aqueous solution) of NaOH wasadded dropwise into the mixture over 30 min. The resulting mixture wasstirred for an additional 3 h at 65° C. and then cooled to roomtemperature. Water (250 mL) was added and the organic solvent wasremoved under reduced pressure. The aqueous solution was adjusted to pHabout 3.0 with conc. HCl, and then heated and stirred at 85° C. for 3 h.It was cooled to room temperature and extracted with MTBE (3×150 mL).The combined organic layer was dried over MgSO₄. Filtration, followed byconcentration, gave 38.5 g (88% by GC purity, yield 79%) of the crudeproduct as yellow oil which was used directly for the next step. ¹H NMR(400 MHz, CDCl₃) δ 10.80 (br s, 1H), 2.51 (s, 2H), 2.30 (s, 2H), 2.08(s, 3H), 0.55-0.45 (m, 2H), 0.45-0.35 (m, 2H); ¹³C NMR (100 MHz, CDCl₃)δ 209.0, 178.2, 49.1, 40.5, 30.0, 20.4, 11.1; MS (m/z) 157.2.

Example 6: Preparation of Methyl [1-(2-Oxo-propyl)cyclopropyl]acetate(Compound 16)

To a solution of [1-(2-oxo-propyl)cyclopropyl]acetic acid (38.5 g) inMeOH (460.0 mL) was added 20.0 g of conc. HCL. The mixture was thenheated to 65° C. and stirred for 3 h. It was then concentrated to removemethanol. A total of 150 mL of water was added and the aqueous solutionwas extracted with MTBE (3×150 mL). The combined organic layer was driedover MgSO₄. Filtration, followed by concentration, gave 34.1 g (84% byGC purity, yield 81%) of the crude product as colorless oil which wasused directly for the next step. ¹H NMR (400 MHz, CDCl₃) δ 3.48 (s, 3H),2.47 (s, 2H), 2.29 (s, 2H), 2.06 (s, 2H), 0.52-0.46 (m, 2H), 0.44-0.37(m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ 208.0, 162.1, 51.2, 49.4, 30.0,11.5; MS (m/z) 170.8.

Example 7: Preparation of Spiro[2.5]octane-5,7-dione (Compound 3)

To a solution of methyl [1-(2-oxo-propyl)cyclopropyl]acetate (12.0 g) inTHF (100 mL) was added 12.1 g of MeONa (30% wt) in MeOH. It was stirredat room temperature overnight. A total of 100 mL of water was added andthe solution was concentrated to remove the organic solvent. Theresulting aqueous solution was extracted with MTBE (3×50 mL) and thenadjusted to pH=2˜3 with conc. HCl. It was then extracted with MTBE (3×50mL). The combined organic layer was dried over MgSO₄. Filtration,followed by concentration, gave the crude product as yellow solid. Tothe crude product was added 12 mL of MTBE, and the slurry was stirred at5° C. for 30 min. The solid was collected by filtration and washed withcold MTBE (2×6 mL). It was dried under vacuum. A total of 4.8 g (62%yield, 98.6% purity by HPLC) was obtained as light yellow solid. ¹H NMR(400 MHz, DMSO-d₆) δ 11.05 (s, br 1H), 5.25 (s, 1H), 2.15 (s, 4H), 0.35(s, 4H); ¹³C NMR (100 MHz, DMSO-d₆) δ 178.61, 103.96, 41.76, 14.95,10.85; MS (m/z) 138.1.

The invention claimed is:
 1. A method of preparingspiro[2.5]octane-5,7-dione having the formula

said method comprising: cyclization of cyclopropylidene carboxylic acidalkyl ester having the formula

with dialkyl 1,3-acetonedicarboxylate having the formula

to form 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acid dialkyl esterhaving the formula

wherein each R may be independently C1-C6 alkyl, and ester hydrolysisand decarboxylation of 5,7-dioxo-spiro[2.5]octane-4,6-dicarboxylic acidto form spiro[2.5]octane-5,7-dione, wherein each R may be independentlyC1-C6 alkyl.